385
FXUS62 KGSP 261331
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
931 AM EDT Wed Jun 26 2024

.SYNOPSIS...
High temperatures peak today ahead of an approaching cold front
Shower and thunderstorm possible over the mountains this afternoon
and chances linger into the weekend. Hot and humid conditions are
expected Friday into the weekend ahead of another cold front
tracking through the area Sunday. Expect slightly cooler
temperatures early next week and an unsettled pattern.

&&

.NEAR TERM /THROUGH TONIGHT/...
Key Messages...

1) Dry and Hot Conditions Linger East of the Mountains Today

2) Isolated Showers and Thunderstorms Expected in the North Carolina
Mountains this Afternoon/Early Evening

3) A Cold Front Tracks Across the Area Overnight into Daybreak
Thursday Increasing Rain Chances, Mainly Across the Mountains


As of 930 AM EDT Wednesday: For the mid-morning update, satellite
shows skies clearing as any low-end clouds in the eastern portion of
the CWA are retreating toward the coastline. Temps are starting to
heat up across the area and headed towards a hot day for the area.
Other than a few minor tweaks to PoPs and T/Td, no major updates at
this time.

Cirrus will continue to spread across the area through the near term
and dry conditions will linger for most locations through this
evening. The exception being the North Carolina mountains where
isolated showers and thunderstorms are expected to develop this
afternoon and early evening ahead of an approaching cold front. CAMs
show the potential for some isolated convection also developing east
of the mountains late this afternoon but confidence on this is too
low for mentionable PoPs at this time. Thus, only have chance PoPs
(35% or less) across the NC mountains for now. The severe threat
will remain low thanks to deep shear values around 15 kts or less
and SBCAPE generally less than 1500 J/kg across the mountains. With
SW`ly 850 mb flow in place ahead of the front, highs today may end
up being the hottest we have seen so far this year and around 8-10
degrees above climo. Temps should easily rebound back into the lower
90s in the mountain valleys, climbing into the mid to upper 90s east
of the mountains. Heat indices should reach into the lower 100s for
some locations along the I-77 corridor (where dewpoints will not mix
out as much) but should remain below Heat Advisory Criteria. Heat
indices elsewhere should generally remain below triple digits as
dewpoints are expected to mix out more west of I-77. Another sparse
cumulus field should develop again this afternoon before dissipating
around sunset.

The cold front will track over the area tonight into daybreak
Thursday increasing rain chances, mainly across the mountains.
However, CAMs seem to agree that activity will hold together
somewhat coming off the mountains. Confidence on activity holding
together east of the mountains remains too low at this time so
confined mentionable PoPs (40% or less) to the mountain zones for
now. Lows tonight will be slightly warmer thanks to cloud cover and
precip, ending up around 7-9 degrees above climo.

&&

.SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/...
As of 130 AM Wed: A trough will cross the Midwest/Northeast Thursday
into early Friday, with continental high pressure migrating eastward
in its wake. In turn, a weak cold front will just reach the CWA on
Thursday. Most models depict height falls occurring more strongly to
our southwest, possibly as a result of an MCV diving into the Deep
South following convection in the Ozarks.  For this reason it looks
like the CWA will get a decent shot of DPVA on Thursday, along with
deep mid to upper level moisture. The low could be in position to
enhance low level moisture flux via onshore flow, but models also
hint at a possible secondary low developing along the sea breeze
front Thu afternoon, where CAM response is noted. Over our area, QPF
response is really pretty unremarkable given the number of factors
one might see at first glance. Perhaps this can be attributed to
winds not being very strong at any level, so there just may not be
enough frontogenetic or dynamic forcing to make much of a difference.
At any rate, with at least modest instability through a fairly deep
layer, the lower heights, and the return of seasonable moisture, at
least chance PoP will be included in all zones. PWATs should top out
near 2 inches, and with slow storm motion localized excessive
rainfall will be a concern. Chances linger into Thu night across the
SE half of the area, where either the sea breeze convection could
continue, or where the inland low/shortwave would still be providing
lift.

The front loses steam and appears likely to stall across TN/NC
Thursday night, with the sfc high pushing off the Northeast coast by
Friday afternoon. At 500 mb only a weakness remains of the trough,
with heights beginning to rise again by evening. What remains of the
front will be reactivated ahead of the next low moving into the Great
Lakes. Southerly or southeasterly flow should continue and dewpoints
will trend higher.  Drying will occur above 700 mb but this air would
appear too high to reach by diurnal mixing, so only a very minor
diurnal dip in dewpoints is expected. Flow remains weak through the
column, so overall we get back into a pattern like we saw early in
the week, with some instability but not much to promote initiation
aside from the southerly flow into the mountains and perhaps little
to sustain deep updrafts. Somewhat lower PoPs will be advertised. If
storms do kick off, owing to the drier air aloft we`ll trade some of
the heavy rain concern for the possibility of wet microbursts, if we
can eke out enough instability. Max temps will be fairly similar to
Thursday, remaining several degrees above normal, but dewpoints are
expected to trend a little higher, so heat concerns would appear to
increase. Low-level flow will amplify Friday night as pressure
gradient strengthens around the Great Lakes system. Most models show
an uptick in QPF overnight, presumably as this initiates elevated
convection.

&&

.LONG TERM /SATURDAY THROUGH TUESDAY/...
As of 230 AM Wed: Cyclone will continue to track just north of the
US-Canada border, carrying another front thru the Ohio Valley and
into the Southeast late in the weekend. Dynamic forcing within the
surrounding trough looks to remain well north of the CWA. Prefrontal
convergence however should promote convective development across the
southern Appalachian region on Saturday, and marked height falls will
occur Sunday. Showers/storms appear likely over most of the area that
day. Although cloud cover should keep temps in check, moisture
pooling will result in soupy dewpoints and heat index probably
peaking for the period, in the low 100s across much of the Piedmont.
PWATs will be even more anomalously high compared to the Thursday
front, likely more than 2 SD above climo, with especially weak flow
through the column, and thus excessive rainfall and localized flash
flooding are possible (especially where soils remain wet from precip
late this week).  There remains some timing variation among the major
model solutions, but generally it appears the front will pass Sunday
night allowing continental high pressure to work into the area from
the NW. Deep drying will occur in time for temps to return to about
normal Monday along with lower dewpoints mixing out to the lower 60s
or upper 50s in most areas.  PoPs that day fall to the 20-40% range,
but focused mainly across the southern half of the area. Temps remain
near normal Tuesday although the sfc high by then will center over
the Mid-Atlantic coast and southerly moisture flux will begin again,
with a deep ridge or anticyclone forming over the lower MS Valley for
midweek. Precip chances will be a little below climo Tuesday.

&&

.AVIATION /14Z WEDNESDAY THROUGH SUNDAY/...
Key Messages...

1) Mostly Dry and VFR through the 12Z TAF period

2) Isolated SHRA/TSRA Will Develop Ahead of a Cold Front this
Afternoon and Early Evening in the North Carolina Mountains

3) The Cold Front Tracks Over the Terminals Overnight into Thursday
Morning Bringing -RA to KAVL

At KCLT and elsewhere: Mostly dry and VFR across the terminals
through the 12Z TAF period. Sfc high pressure will remain in place
through this morning as a cold front approaches out of the
northwest. Winds are mostly calm to light and VRB this morning.
Winds will gradually pick up out of the S/SSW later this morning
into early this afternoon, with speeds ranging from 4-7 kts east of
the mountains. Cirrus continue pushing in from the north this
morning and are mainly impacting KAVL. Cirrus will continue to
increase through the 12Z TAF period. Isolated diurnal SHRA/TSRA will
develop ahead of the cold front, mainly across the NC mountains.
Thus, maintained the mention for VCSH at KAVL, with dry conditions
elsewhere through the TAF period. Some of the high-res guidance has
some isolated SHRA/TSRA developing east of the mountains late this
afternoon but confidence on whether this will track directly over a
terminal remains too low to mention. Another sparse diurnal VFR
cumulus field will develop once again today. The cold front will
track over the terminals tonight into Thursday morning leading to a
line of -RA. Only have VCSH mentioned at KAVL overnight as the -RA
will reach this terminal first. -RA may not reach the terminals east
of the mountains until after the 12Z TAF period so maintained dry
conditions elsewhere for now. Winds will go light again tonight,
remaining S/SSW east of the mountains ahead of the front. Winds at
KAVL will turn NW overnight while winds turn NE early Thursday
morning at KHKY and KCLT behind the front.

Outlook: A cold front will continue tracking over the terminals
early Thursday before stalling south of the area on Friday, keeping
SHRA/TSRA chances around the region. Another cold front will impact
the terminals this weekend keeping unsettled weather around.

&&

.GSP WATCHES/WARNINGS/ADVISORIES...
GA...None.
NC...None.
SC...None.

&&

$$

SYNOPSIS...CP
NEAR TERM...AR/CP
SHORT TERM...Wimberley
LONG TERM...Wimberley
AVIATION...AR